1. Technical Field
The present invention relates to a disk drive apparatus as typified by a hard disk drive and more particularly to position control of a head that reads or writes data in a disk drive apparatus.
2. Description of the Related Art
The hard disk drive is one of the most widely used external storage for computers. As is well known, the magnetic disk, which is a storage medium of the hard disk drive, uses a sector as the smallest unit of data recording: a disk surface is divided concentrically into tracks, which are further divided radially into sectors. The nearer to the circumference of the magnetic disk, the higher the track recording density can be made. Therefore, zone bit recording (Zoned Bit Recording), which is the mainstream data recording method for magnetic disks, groups all the tracks into a number of zones and keeps the track recording density within each zone constant. Since a sector is normally 512 bytes long, the nearer to the circumference of the magnetic disk, the more sectors the track contains.
The hard disk drive has a magnetic head for reading or writing data from/to the magnetic disk. The magnetic head is mounted on an actuator mechanism which swings by means of a VCM (Voice Coil Motor). When the magnetic head reads or writes data, the actuator mechanism operates to move the magnetic head to a designated track and position it there. The process of moving and positioning the magnetic head is known as a seek. The magnetic head seeks to a designated track based on servo information stored on the magnetic disk.
As described above, the tracks on the magnetic disk are divided into a number of sectors. Each sector constitutes a data area where data is stored. Besides, the magnetic disk contains servo areas where servo information is stored. The servo areas store track identification information and burst patterns as the servo information. The track identification information represents the addresses of individual data tracks. It is read by the magnetic head to determine the track where the magnetic head is currently located. The burst patterns consists of an array of multiple signal storage areas out-of-phase to each other. The areas, each of which stores signals are laid at regular intervals in the radial direction of the magnetic disk. The signals output from the burst patterns makes it possible to determine the amount of deviation of the magnetic head from data tracks. When data is read from or written to the magnetic disk, which is rotating, position control is performed by checking the position of the magnetic head based on the servo information and driving the actuator mechanism and thus the magnetic head so as to correct any deviation.
3. Problems to be Solved by the Invention
When a magnetic head reads or writes data to/from a designated track on a magnetic disk, the positioning accuracy of the magnetic head comes into question. With recent improvement in the recording density of magnetic disks, there is demand for high positioning accuracy. The factors that impair the positioning accuracy of magnetic heads include disturbances. It is pointed out that disturbances can be caused by the tare weight of the actuator mechanism itself, the elastic force of flexible cables attached to the actuator mechanism, etc. In view of this, various techniques for positioning magnetic heads accurately have been proposed.
Data is read or written only after it is verified that the magnetic head is positioned accurately on a designated track. Therefore, even if a data read or write command is given, a data read or write must wait until the magnetic head is positioned. The positioning control techniques proposed so far have reduced the wait time for data reads/writes. However, it is reported that improved recording density has made it impossible to avoid the wait time for data read/write operations even with the positioning control techniques proposed so far.
Thus, it is an object of the present invention to provide a technique that can reduce the wait time for data read/write operations even on high density magnetic disks.